A need exists for a verification device which would serve to identify, for example, personnel desiring entry into a secured area. It would be desirable to offer entry at various gates which would not need to be manned by security guards but where the identity of a person seeking entry or exit from such an area must be assured before such entry or exit.
One of the solutions toward assuring identification in such situations is that of signature verification. An individual desiring entry or exit utilizes a special writing instrument and/or special writing platen, either one of which produces electrical outputs in response to the individual's action of writing his signature, the outputs being dynamically representative of selected aspects of the handwriting action producing the signature. These outputs are compared to other outputs representative of past, sample or exemplary signatures from a data bank, such as a computer memory. This may be done by utilizing any one of a number of known computer programs in general purpose or special computers or hardwired comparator apparatus to verify with a high degree of accuracy that the individual submitting the signature is or is not the person he represents himself to be.
Several varieties of signature verification systems are known or are commercially available. One of these, disclosed in U.S. Pat. No. 3,983,535 to Herbst et al, utilizes input signals proportional to accelerations of the writing stylus in either "x" or "y" directions or both. The signals are in turn proportional to the muscle forces exerted by the signer, and are of predetermined consistant durations when performing particular strokes in a habitual signature. U.S. Pat. No. 3,983,535 suggests for use as input devices such commercially available x-y tablet or platen devices as typified by those disclosed in U.S. Pat. No. 3,668,313 to Dym and U.S. Pat. No. 3,582,962 to Mazza. However, each of the above noted x-y tablet devices produces analog signals proportional to x-y pen displacement or position and it is necessary to generate the second derivative with respect to time of pen displacement in order to obtain the acceleration information required for input to the system of U.S. Pat. No. 3,983,535.
A second variety of signal verification system is shown in U.S. Pat. No. 3,962,679 to Engelbrecht. The discriminant or input signal to this system is proportional to handwriting speed, where handwriting speeds is defined as the scalar magnitude of velocity or EQU S = .sqroot. V.sub.x.sup.2 + V.sub.y.sup.2,
where V.sub.x and V.sub.y are the x and y velocity components, respectively, of the velocity of a stylus with respect to a writing surface. Also disclosed in this patent are optional additional or alternative discriminants in the form of a magnetic stylus and a platen capable of output signals proportional to handwriting pressure as well as V.sub.x and V.sub.y velocity components.
A third type of signature verification system which uses an input signal representing the variable pressure between a stylus and a writing surface exerted by a subject when writing a signature is disclosed in U.S. Pat. No. 3,959,769 to Sternberg et al. This patent discloses a pressure transducer which can consist of a stylus or pen having a strain gauge and a resistance bridge structure for generating an output voltage having an amplitude which varies as a function of the pressure exerted between the stylus and writing surface. Another input device comprising a pressure transducing platen for use in a signature verification system, such as that disclosed in U.S. Pat. No. 3,959,769, is described in U.S. Pat. No. 3,991,402 to Radcliffe, Jr. The device thereof employs a magnetic transducer to sense displacements of a writing platen along the z axis only, such displacements being proportional to the z-axis, i.e., downward, component of pressure or force exerted on the platen by handwriting.
An input device for a signature verification system which produces output signals proportional to x, y and z components of handwriting force is described in U.S. Pat. No. 3,988,934 to Kamphoefner et al. Their device consists of a writing platen suspended by a pair of thin horizontal beams to an intermediate surrounding structure. The intermediate structure is suspended by a similar pair of vertical beams to a rigid frame. The supporting beams for the writing platen and the intermediate structure have strain gauges attached to measure handwriting forces in the x, y and z directions. The x, y and z displacements of the supporting beams are proportional to the corresponding handwriting forces on the writing platen.
Input devices for signature verification systems cited above or otherwise known in the art comprise writing styli and/or platens which are sensitive to handwriting pressure, velocity, speed or acceleration or combinations thereof. These input devices employ transducers which need separate voltage or current sources such as strain gauges or magnetic transducers. In general, strain gauge transducers must be carefully selected and matched and are usually employed in resistive bridge circuits which require careful balancing. Such devices are generally expensive and vulnerable to damage through normal use or by inadvertant shock which may occur by dropping, etc., during normal use. Strain gauges must be bonded to somewhat flexible members because of their inherent insensitivity to very small strains. Magnetic devices are almost always cumbersome, susceptible to stray magnetic fields and expensive to fabricate.